Staff

Abstract:
We have designed and built low-cost compact ultrasound imaging-guided robotic HIFU (High-Intensity Focused Ultrasound) ablation device for thermal damage of solid tumors in small animals. Before this device is used to treat animals, experimental studies on ex vivo tissues were necessary to assess the accuracy of its targeting, ensuring the safety of therapy. The objective of this study was to assess the targeting accuracy of our device in the focal and axial plane of the HIFU beam using ex vivo tissue embedded in a reference cylindrical chamber inside which a coaxial cylindrical volume with a smaller diameter was ablated. HIFU beams with selected acoustic parameters, generated by a singe-element bowl-shaped 64-mm HIFU transducer operating at 1.08 MHz or 3.21 MHz frequency, were propagated in two-layer media: water-tissue (50 mm-40 mm) and focused at 12.6-mm depth below the tissue surface. Cylindrical necrotic lesions of various size were created by moving the chamber using a computercontrolled precise positioning unit. Lesions formed were compared with those intended for treatment using various visualization methods and displacement between their centers were determined. The targeting accuracy in the focal and axial planes was found to be respectively about 98% and 86% when determined from photos and about 88% and 76% when determined from MR images. The displacement between the centers of the necrotic lesion formed and planned for treatment was about 1 mm in the focal plane and about 2 mm in the axial plane. Our ablation device can be used as an effective and safe tool to plan, monitor and treat solid tumors in small animals and to test new anti-cancer drugs in preclinical studies.

Abstract:
We have designed and built ultrasound imaging-guided HIFU ablative device for preclinical studies on small animals. Before this device is used to treat animals, ex vivo tissue studies were necessary to determine the location and extent of necrotic lesions created inside tissue samples by HIFU beams depending on their acoustic properties. This will allow to plan the beam movement trajectory and the distance and time intervals between exposures leading to necrosis covering the entire treated volume without damaging the surrounding tissues. This is crucial for therapy safety. The objective of this study was to assess the impact of sonication parameters on the size of necrotic lesions formed by HIFU beams generated by 64-mm bowl-shaped transducer used, operating at 1.08 MHz or 3.21 MHz. Multiple necrotic lesions were created in pork loin samples at 12.6-mm depth below tissue surface during 3-s exposure to HIFU beams with fixed duty-cycle and varied pulse-duration or fixed pulse-duration and varied duty-cycle, propagated in two-layer media: water-tissue. After exposures, the necrotic lesions were visualized using magnetic resonance imaging and optical imaging (photos) after sectioning the samples. Quantitative analysis of the obtained results allowed to select the optimal sonication and beam movement parameters to suport planning of effective therapy.

Keywords:
automated ultrasound imaging-guided HIFU ablation system, ex vivo tissue, ultrasonic exposure parameters, extent of necrotic lesions

Abstract:
This study reports the quantitative, precise and accurate results of nanoscale friction measurements with the use of an Atomic Force Microscope calibrated with a precise nanoforce sensor. For this purpose, three samples of spin-coated thin Polymethylmethacrylate (PMMA) films were prepared with the following thicknesses: 235, 343, and 513 nm. Three different AFM probes were used for the friction measurements: with diamond-like carbon (DLC) tip with a small (15 nm) or big (2 µm) tip radius, and a reference silicon tip with a small (8 nm) radius. The results show that in all of the studied cases, the coefficient of friction strongly depends on the applied load, being much higher for a lower load. Furthermore, a strong relation of the friction force on the cantilever's geometry, the scanning velocity, and the film thickness was observed.

Keywords:
lateral force microscopy, friction, thin PMMA films, atomic force microscope, DLC coatings, adhesion

Abstract:
In this paper, the mechanical properties of composites consisting of electroplated Ni and co-electrodeposited SiC particles, coated with a thin protective layer of Ni, were studied. The protective layer was on the SiC particles prior to adding them to the electrolyte bath. It was demonstrated that due to the application of the protective layer it was possible to decrease sliding friction force, and improve the wear resistance, of the composite coatings in comparison with standard electroplated composite coatings made of Ni and co-electrodeposited pure SiC particles. Coating SiC particles with Ni was achieved by means of a PVD process. The main advantage of this step is avoiding oxidation of the surface of the particles during the contact with an electrolyte. Particles protected from oxidation lead to stronger interfacial bonding between the matrix and the reinforcement. Furthermore, better bonding protects the SiC particles from being extracted from the matrix by a counter-probe during friction and wear tests. The influence of the particle's concentration is studied. A smaller friction force and constant wear rate was observed.

Keywords:
wear, friction, interfacial bonding strength, metal matrix composites, silicon carbide, electrodeposited nickel

Abstract:
In this paper, the study of the mechanical properties of composites consisting of electrodeposited Ni and co-electrodeposited SiC particles coated with a thin Cu layer was presented. It was demonstrated that the coating allowed to increase the concentration of ceramic particles in the composite. Although the plating parameters were the same for both types of composites, the concentration of SiC was 15% for the composite containing coated particles (Ni/SiC-Cu) and 10% for the composite containing uncoated particles (Ni/SiC). Furthermore, tensile tests showed that the Ni/SiC-Cu samples exhibited higher Young's modulus than the pure electrodeposited Ni samples or Ni/SiC samples. The measured Young's modulus of the Ni/SiC-Cu composite was 250 ± 10 GPa. However, the ultimate tensile strength of the Ni/SiC-Cu composite was lower than that of pure Ni. To explain the mechanical behaviour of the Ni/SiC-Cu composite, the microstructure of the interface of this composite and its bonding strength were studied. Microstructure studies conducted using a scanning electron microscope (SEM) revealed that the SiC/Cu interface was smooth and of good quality whereas the Cu/Ni interface was rough but also of good quality. The measured bonding, normal, and shear strength values demonstrated that the SiC/Cu interface was weak, and that was the main reason for the low ultimate tensile strength of the composite. The shear strength of the SiC/Cu interface was measured using a novel method: micropillars shearing including atomic force microscopy (AFM). Finally, a simple finite element model of the Ni/SiC-Cu composite, based on cohesive elements, was developed.

Keywords:
Interfacial bonding strength, Metal matrix composites, Tensile strength, Silicon carbide, Electrodeposited nickel

Abstract:
In this paper, we present a device which is very sensitive for small changes in the viscosity of the investigated fluid. The main part of the device is a piezo-electric bimorph which consists of the brass shim with two piezo-ceramic layers on the opposite sides. One of them is responsible for generating vibrations, whereas the second one is meant to measure system response which is produced by the damping properties of the surrounding fluid. During the experiment, the cylindrical bar is forced to move by the series of sinusoidal waves with different frequencies and at constant amplitudes. The probe is immersed in the fluid and then the amplitude vs frequency and phase vs frequency curves are obtained. Next, one can determine the viscosity according to a proper mathematical model. The resonant frequency is related to the damping coefficient which depends on the viscosity of the surrender fluid and immersion depth of the probe. The coefficients necessary for calculating viscosity are obtained by fitting the resonance curve to the amplitude vs frequency data obtained from the experiment. The device has been applied to study the anisotropy of magnetorheological fluids. The weak anisotropy of viscosity has been observed. The highest value of viscosity was observed in the case of viscosity measurement in the direction orthogonal to the magnetic field and the lowest in the direction parallel to the magnetic field.

Abstract:
The wear of contacting silicon surfaces in microelectromechanical systems (MEMS) has been a longstanding concern. To address this issue, the effects of immersing silicon surfaces into alkali metal chloride solutions (LiCl, NaCl, CsCl) on their sliding friction and wear were investigated. A custom-built reciprocating tribometer was used with a sapphire ball as the counterbody. Results indicated that the friction coefficient between the silicon surface (p-doped, orientation (100)) and a sapphire ball can be reduced by up to 30% by treating the silicon surfaces in aqueous salt solutions (concentration 1 mol/L, exposure for 24 h). These modified surfaces also have higher wear resistance and a significant change in wettability. After immersion, the contact angle between the silicon surface and water was reduced by approximately 50%. These results may lead to new, simple, and inexpensive methods to increase the wear resistance of silicon surfaces for use in MEMs devices.

Keywords:
silicon surface, wear, friction, alkali metal chlorides

Abstract:
In this paper we present a simple and direct method for the lateral force calibration constant determination. Our procedure does not require any knowledge about material or geometrical parameters of an investigated cantilever. We apply a commercially available microforce sensor with advanced electronics for direct measurement of the friction force applied by the cantilever's tip to a flat surface of the microforce sensor measuring beam. Due to the third law of dynamics, the friction force of the equal value tilts the AFM cantilever. Therefore, torsional (lateral force) signal is compared with the signal from the microforce sensor and the lateral force calibration constant is determined. The method is easy to perform and could be widely used for the lateral force calibration constant determination in many types of atomic force microscopes.

Keywords:
A precise and direct method for lateral force calibration, Inaccuracy equal to approximately 2%, Wedge method is proven to give inaccurate results

Abstract:
In Poland cancer is the second cause of death overall, and the first before 65. Demand for new anticancer therapies is increasing every year. The main objective of studies on medical and technical aspects of new anticancer methods is to reduce unwanted side effects and costs associated with conventional methods of treatment. Percutaneous (noninvasive) HIFU (High Intensity Focused Ultrasound) technique gives the chance to radically reduce both of these factors. The main goal of this work is automation of HIFU technology for producing thermal damage to the entire volume of a solid breast tumor implanted into a rat mammary gland using the proposed bi-modal ultrasound equipment, enabling the ultrasonic heating of a small volume within the tumor under the ultrasonic imaging control, as well as 3D scanning of the heating beam focus throughout the entire tumor volume. Design of the proposed equipment includes the heating probe of low frequency (about 1MHz), allowing penetration of pulsed focused waves into tissues, and the linear phased array probe of high frequency (from 4 MHz to 10 MHz), allowing visualization of the locally heated area inside the tumor in real time. Automatic 3D scanning of the heating beam focus provides the thermal damage to its entire volume.

Keywords:
High Intensity Focused Ultrasound beam, focal volume, tissue damage

Abstract:
A material strength depends on its microstructure, which in turn, is controlled by an engineering process. Quantification strongly depends on the characteristic length scale of a particular
microstructure. This microstructural, or intrinsic, size governs the mechanical properties and post-elastic material deformation at all sample dimensions, as the classical definition of ultimate tensile strength deems it to be an intensive property, therefore its value does not depend on the size of the test specimen. However, in the last years, the vast majority of uniaxial deformation experiments and computations on small-scale structures unambiguously demonstrated that at the micron and sub-micron scales, this definition no longer holds true. Study focuses on the both the intrinsic (i.e. microstructural, internal size effect) and extrinsic (i.e. sample size, external size effect) dimensions which play a non-trivial role in the mechanical properties and material deformation mechanisms, it is critical to develop an understanding of their interplay and mutual effects on the mechanical properties and material deformation, especially in small-scale structures. To obtain its properties and the influence of scale in this study, nanopillars made from silicon was made and then tested under atomic force microscope in lateral force microscopy (LMF) mode. The nanopillars were sheared using AFM probes and then with knowledge of shear force the mechanical properties were obtained. Nanopillars varied in pillar diameter and grain size. The study is focused on the investigation of mutual dependence fracture strength due to grain size and pillar diameter.

Abstract:
Method for lateral force calibration in AFM and its applications.

Abstract:
Viscosity is a very important property of thin polymer films used in modern microelectronic technology i.e. in nanoimprint lithography. Hence, in this work we present a method for viscosity of ultrathin polymer films determination. The viscosity is evaluated from the response of the oscillating piezoelectric cantilever at the end of which an indentation probe is mounted (Fig. 1a). When a polymer film is indented, the resonant frequency of the oscillations is changed and the parameters of used model (i.e. Maxwell model) can be identified. The frequency of the oscillations is equal to tens of kilohertz therefore the influence of extremely high deformation velocities can be investigated by means of this method. It is also possible to conduct the experiments in elevated temperature (up to 150 o C). The oscillations direction can be parallel as well as perpendicular to the fil m’s surface. The investigated films were made of PMMA. Their thickness ranges from a few nanometers up to 1 micrometer. The results were compared with other methods of the viscosity determination: the investigation of the creep response during nanoindentation, sinus mode nanoindentation and atomic force microscope based technique